With the recent trend toward widespread use of mobile devices such as cellular phones and achievement of higher speed and higher frequency in semiconductor devices serving as main components for personal computers, there is an ever increasing demand for a multilayer ceramic capacitor having a smaller size and a higher capacitance, the multilayer ceramic capacitor being implemented in such electronic devices. To provide such a multilayer ceramic capacitor, attempts have been made to reduce the thickness of dielectric layers constituting a multilayer ceramic capacitor and to increase the number of dielectric layers stacked.
For example, Patent Document 1 describes use of a mixture of a barium titanate powder (BCT powder) in which the A site is partially substituted by Ca and a barium titanate powder (BT powder) containing no Ca as dielectric powders constituting a dielectric ceramic. Such a combined use of two dielectric powders provides a multilayer ceramic capacitor in which fired dielectric layers are constituted by composite grains of crystal grains having a Ca concentration of 0.2 atomic % or less and crystal grains having a Ca concentration of 0.4 atomic % or more, both types of crystal grains containing barium titanate as the main component; and the thickness of the dielectric layers is reduced to 2 μm.
However, the multilayer ceramic capacitor disclosed in Patent Document 1 above and having dielectric layers constituted by the composite grains has a problem in that the insulation resistance gradually decreases while the capacitor is left in a high temperature environment for evaluation of the high temperature loading life.
Additionally, when the multilayer ceramic capacitor is produced, a capacitor body immediately after firing at a temperature of about 1200° C. in a reducing atmosphere and before formation of external electrodes has dielectric layers that are reduced and do not have practical insulation resistance and have a low relative dielectric constant.
For this reason, such a fired capacitor body generally needs to be subjected to a reoxidation treatment at a lower temperature than the temperature of the firing and in an atmosphere having a higher oxygen concentration than the oxygen concentration of the atmosphere used in the firing.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-156450
It is an object of the present invention to provide a multilayer ceramic capacitor that suppresses a reduction in insulation resistance with time during a high-temperature load test and a high insulation resistance after firing.